Amplifying scheme for photocathodes



1 June 18, 1940. o. KRENZIEN 2,205,207

- AMPLIFYING SCHEME FOR PHOTO-CATHODES Filed June 16, 19s? 2 Sheets-Sheet 1 Fi.j. K j 0 0 200 5 &

illlllll ""w an v. 70 m n an M n M 1440 WITNESSES: INVENTOR W/ Otto lfreizzzezz.

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' ATTORN Y June 18, 1940- o. KRENZIEN 4 AMPLIFYING SCHEME FOR PHOTO-CATHODES 2 Sheets-Sheet 2 Filed June 16, 1957 INVENTOR Oflo K767721677.

WITNESSES:

ATTORNEY Patented June 18,1940

UNITED STATES AMPLIFYING SCHEIWE FOR PHOTO- CATHODES Otto Krenzien, Berlin-Siemensstadt, Germany,

assignor to Siemens & Halske; Aktiengesell- 'schaft, Berlin, Germany, a corporation of Germany Application June 16, 1937, Serial No. 148,451 In Germany June 13, 1936 6 Claims.

The invention relates to discharge devices and especially to the type of discharge device known as secondary emission amplifier tubes or multipliers. I

An object of the invention is to provide a secondary emission amplifier tube that not limited to the application of magnetic fields.

Another object of the invention is to provide an amplifying device in which the structural parts do not shadow one another to any extent.

Other objects and advantages of the invention will be apparent in the following description and drawing in which:

Figures 1 through 5 are views, partly in crosssection and partly in elevation, of various modi fications of electrode structure embodying the invention.

To increase the electron current delivered by a cathode in the known secondary emission amplifier tubes or multipliers, the capability of fast moving electrons in effecting the release of secondary electrons on impinging on a plate under a suitable positive potential and suitably activated is applied. By repeated use of this secondary emission effect in a plurality of steps following each other, considerably increased electron currents, as compared with the cathode cur-.

rent, may, as is known, be attained in the end stages.

To attain a good effect in such amplifying tubes operating with secondary emission, it is essential that the electron ray be so influenced that as high a proportion as possible of the electrons produced at the individual electrodes at i any instant shall impinge on the following electrode at the higher potential and result in the production of further secondary electrons.

Further details of the preferred construction of the electrode system according to the invention will be seen from the attached figures in which the equi-potential lines for different arrangements and the potential dimensioning are indicated. The number values on the individual lines give the potential increase in volts, which are determined with reference to a zero level for the corresponding positions of the electric field. The potential distribution is attained in known manner by measuring the individual systems in electrolytic water troughs. The illustration of individually calculated electron paths is out of the question, since the initial speed of the secondary electrons is distributed over too'wide a range. The electric field lines, which the electrons follow strictly only if they have no initial -velocity, are not illustrated; they are always naturally perpendicular to the equi-potential lines.

Figure 1 shows a known embodiment of a secondary emission amplifier in which the photocathode K has the lowest potential and the secondary emission electrode S is at a medium potential between the cathode K and the anode A. The impinging light bundle is to be regarded as projected from below in this view as also in the following. It appears from the potential distribution that only electrons which leave the middle of the cathode K reach the secondary emission electrode S and produce an increase in the electron stream, while the other electrons impinge directly on the anode A.

In Fig. 2, a grid-shaped secondary emission electrode S according to the invention is reproduced. Corresponding to the potential distribution, a large proportion of the photo-electrons released at the cathode K impinge on the grid electrode S and produce a strengthened secondary electron current. electrons will naturally pass by S and arrive directly at anode A, i. e., this portion is not subjected to strengthening by the released secondary electrons at the electrode S.

From the position of the equi-potential lines in Fig. 3, it is further to be noted what advantage can be attained if in accordance with the further aspects of the invention also grid-shaped guiding electrodes F are present in addition to secondary emission electrode S. By the additional use of a guiding electrode F under negative potential, good guiding of all the primary electrons to the secondary emission grid S is effected and with it the production of a large number of secondary electrons is made possible. As appears, however, at the same time from Fig. 3, a good multiplication or amplifying effect is in this case not completely attained for the drawn potential lines make possible the realization of the fact that the secondary electrons released at S must overcome a counter-field before reaching the accelerating field of the anode A, i. e., the secondary electrons which leave S with a small initial velocity are braked and in general may not lead to an increase in the photo-electric current. In such a secondary emission amplifier, it is, therefore, important with reference to the arrangement of the grid to provide that for the given potential differences between the individual electrodes the secondary electrons at once after their production come into an accelerating field. This may take place by properly selecting the attractive power (of one electrode through an 'other-such as an anode through a grid) of those electrodes which take part in the building up of the potential field before the electrodes in question.

To increased extent the potential distribution between the individual electrodes is naturally to be given attention if the produced secondary emission current is not conducted at once to the anode, but in its turn should serve as primary current on a further grid electrode to release A considerable number of secondary electrons. In Figs. 4 and 5, such electrode arrangements serving as plural stage amplifiers are reproduced with the measured potentials. While in the arrangement, in Fig. 4, in the direction of the succeeding amplifying stage, the harmful potentials which are more negative than the secondary emission electrodes, are manifested and produce a braking of the secondary electrons (compare, for example, the indicated equi-potential line for 130 volts between the grid S2 at 150 volts potential and the grid S3 at 200 volts potential), in Fig. by reason of the selection of a smaller attractive power of the negative guiding grids F1-F4, no such potential swells for the secondary electrons are present, i. e., the secondary electrons find at once at their emission an accelerating field to the next secondary emission step. In Figs. 4 and 5, four successive secondary emission amplifier steps are shown. The cathode K is constructed as a hollow body with an interior active surface so that it may operate for light rays similar to a black body, 1. e., a maximum utilization of the impinging light is yielded. Leads are indicated also in Fig. 5 for connecting groups of control elements such as S and S etc., and also groups of the second set of elements F1, F2, etc., whereby a suitable source of operating potentials may be applied to the electrodes. In order to give a better picture of the electrical field stresses between electrodes, these leads are omitted in the other figures. In this manner, possible confusion of stress lines and lead lines is avoided. It is understood, of course, that grid electrodes of all figures are to be brought out as shown in Fig. 5.

Since the struts of the individual grids are also photo-electrically activated, photo-electrons are produced in them also which under certain circumstances reach the individual amplifying stages and in all cases, add to the increase of the final current, so that the shadowing of the oathodo by the individual grid struts is still further essentially decreased in its significance.

The potential dimensioning for the individual successive steps are naturally adapted to the general potential level which increases as the anode is approached and are to be derived numerically in their details in the figures from the indicated equipotential lines.

An essential advantage of the electrode arrangement according to the invention lies in the fact that the secondary emission electrodes have a relatively large surface.

I claim as my invention:

1. A discharge device comprising an envelope having a first electrode capable of emitting charges when subjected to the influence of a beam of radiant energy, a second electrode capable of emitting additional charges when charges emitted by said first electrode impinge thereon, a third electrode for collecting the charges emitted by said first and second electrodes and a fourth electrode for causing a maximum. proportion. of the charges emitted by said first electrode to impinge on said second electrode, said second electrode being interposed between said first and third electrodes and comprising a latticed grid structure, with the elements bounding the lattice openings disposed with their smallest surface areas pointing directly towards and away from the direction in which a beam of radiant energy is to be projected on said first electrode and said fourth electrode comprising a latticed-grid structure electrically'separate from said second electrode and having its bars positioned between the bars of said second electrode.

2. A discharge device comprising an envelope having a first electrode capable of emitting charges when subjected to the influence of a beam of radiant energy, a second electrode capable of emitting additional charges when charges emitted by said first electrode impinge thereon, a third electrode for collecting the charges emitted by said first and second electrodes, and a fourth electrode for causing a maximum proportion of the charges emitted by said first electrode to impinge on said second electrode, said second electrode comprising a plurality of bars and said fourth electrode comprising an other plurality of bars positioned between the bars of said second electrode and electrically insu ated therefrom.

3. A discharge device comprising an envelope having a first electrode capable of emitting charges when subjected to the influence of a beam of radiant energy, a second electrode capable of emitting additional charges when charges emitted by said first electrode impinge thereon, a third electrode for collecting the charges emitted by said first and second electrodes and a fourth electrode for causing a maximum proportion of the charges emitted by said first electrode to impinge on said second electrode, said second and fourth electrodes being interposed between said first and third electrodes and comprising latticed grid structures, with the elements bounding the lattice openings disposed with their smallest surface areas pointing directly towards and away from the direction in which a beam of radiant energy is to be projected on said first electrode, the lattice-bars of said fourth electrode being positioned between the bars of said second electrode and being electrically insulated therefrom.

4. Apparatus according to claim 2, characterized by the fact that the first electrode has a coating of emissive material and the second and fourth electrodes are similarly coated.

5. An electrical discharge device comprising an envelope having a cathode which is electron-responsive to radiant energy, an anode, control means intervening between said cathode and anode and comprising a first set of bars and a second set of bars positioned between said first set and electrically independent thereof, conductor means connected to said first set of bars for applying thereto a positive potential greater than a certain critical value, and conductor means affixed to said second set of bars for applying thereto a positive potential less than said critical value.

6. An electrical discharge device comprising an envelope containing a cathode which is electronresponsive to radiant energy, an anode, a first set of control grids comprising a plurality of groups of spaced bars and a second set of control grids comprising a plurality of groups of bars positioned between the first-mentioned bars, leads connected to each of said groups for impressing thereon a positive potential relative to said cathode, said first set requiring a potential more positive than said second set.

OTTO KRENZIEN. 

